This is a photo of the nut, it's a hexagonal nut and I have an Allan key set but don't know which one to use to loosen this.

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3 Answers 3


It's really hard to judge scale from a photo.

$£€ 12 will buy you two sets of allen keys - metric & imperial. they'll last you a lifetime. The upside with allen keys is they only come in quite a limited range of sizes, so sets are reasonably small.
But you do need both sets to be sure. It's not good with allen keys to try use one that almost fits, because if you round it out, then you up the ante into bolt extractors; much more skill required.


Try which key from your set fits in comfortably but still holds a grip. If none of them does, maybe one of the bits that come with electric screwdrivers and can also be bought separately will.


The "12.9" indicates the strength of the bolt (12.9 is very strong), not the size.

But it's normally associated with metric sizes, so if your Allen key set is imperial (inches), it's unlikely any of them will fit correctly.

Try measuring the socket size in millimetres with calipers or a ruler.

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